The Melacha of Potzea Doesn’t Apply to the Murex

On page 17, Dr. Singer discusses the meaning of the word “potze’a”, and he accepts Rabbi Herzog’s understanding that there is a connotation in potze’a of cracking a hard shell. Sad to say, Rabbi Herzog was inexplicably mistaken in this understanding. In both biblical and mishnaic usage, potze’a carries no connotation of a hard object. One of numerous such examples is the Mishnah Ketubot 43b, “Patza’a Bifaneha”, “he wounded her face”. According to the Radak’s Sefer Hasharoshim, Potze’a refers to incising a smooth surface, splitting, cutting, wounding, or causing a fissure. See also Rashi, Shemot 21:25 and Shir Hashirim 5:7. It is the usage of “splitting”, that is found in Shabbat 122b, “Liftzo’a Egozim”, to split, not to crack, nuts.

A small experiment demonstrates why the Gemara there speaks of using a kurnos, a blacksmith’s hammer, for opening nuts. When a walnut is struck smartly with a light ¼ lb. Hammer along the seam where the halves join, the shell at the contact point is crushed. But when it is merely tapped with a heavy 1 ¼ lb. Hammer, it splits in half all the way around.

R’ Yechiel Yitzchak Perr (https://www.tekhelet.com/pdf/0954.pdf)

Hard shell: The Gemara discusses the case of someone who extracts the dye from the chilazon on Shabbat.[40] The verb used by the Gemara in describing the action of the person extracting the dye is potzea. Potzea is usually understood to mean to crush or crack open.[41] This would imply that the chilazon has a hard shell, though this could be an external or an internal shell. Rashi says that the person squeezes (docheik) the chilazon in his hand to get out the blood (dye secretion). From Rashi’s comment we can only infer that squeezing the chilazon can make the dye come out. Rashi’s use of the word “squeeze” is difficult to understand since it seems to imply a soft substance, not a hard shell. This difficulty in understanding Rashi might be resolved if the chilazon, while being held in the hand, has a shell on one side, and flesh on the other. Thus, the person squeezes the fleshy side of the chilazon, and in the process may crack open, or crush, the hard shell on the other side. Murex trunculus has a hard, external shell that is cracked in order to get the dye out. The shell almost completely encloses the body. This would be consistent with the usual understanding of potzea, but not with Rashi’s docheik.

Dr. Mendel Singer (https://www.tekhelet.com/pdf/mendel.htm)